The present invention, in some embodiments thereof, relates to orthoses and, more particularly, but not exclusively, to an ankle foot orthosis.
Drop foot, also known as steppage gait, is a condition in which there is a deficit in pivoting the foot upward toward the anterior of the tibia, herein dorsiflexion, due to neurologic and/or muscular malfunction.
To prevent tripping during swinging forward, herein swing phase of gait, the affected leg must be lifted high off the ground and dropped into place in front of the other foot, referred to as a steppage gait.
In “swing phase” of gait, the drop foot remains in the “dropped”, herein plantiflexed position and often barely clears the ground during the swing phase. As a result, the foot may catch on low lying debris, rocks or even an edge of a pavement stone, causing the person to trip and fall.
A fall, particularly in an osteoporotic older person, can result in life-threatening bone fractures, immobility, and, due to the resultant sedentary life style, an early demise.
Surgical treatment, when applicable, includes muscle transfers and/or nerve implantation; the latter presently limited to nerve lesions near the spinal nerve root.
Conservative therapy includes fitting the user with an ankle foot orthosis (AFO); which lifts the foot with respect to the leg during swing phase of the gait, thereby substantially allowing the foot to clear the ground.
There are aspects of the phases gait that may be beneficial to a user afflicted by drop foot when properly addressed by an AFO; for example pronation and supination of the foot.
Pronation refers to inter alia, the forefoot assuming a substantially parallel position to the ground whereby the foot flexibly adapts to the angle and/or terrain of the ground.
Supination refers to inter alia, the forefoot assuming an angled position to the rear foot in whereby the forefoot forms, what is referred to as a “locked position”. The locked position of the forefoot during supination allows the foot to act as a lever to aid in propulsion associated with the toe off phase of gait.
In the drop foot condition, even with fully non-functional intrinsic and extrinsic foot muscles, the foot assumes “passive” positions of pronation and supination.
For example, when the right leg is in swing phase and through heel contact, the right foot is in preparation to pronate upon contact with the ground.
As the right foot becomes fully planted on the ground, in what is referred to as the “foot flat” position, the left leg is in swing phase while the left side of the pelvis circumducts toward the sagittal body plane. The left pelvic circumduction causes a supination in the right foot, with the supination continuing through right foot toe off.
Following toe-off, the right foot again assumes a position of pronation in preparation for heel contact and foot flat phases of the gait cycle.
To aid in the above-noted passive cycle of pronation and supination in a leg afflicted with drop foot, a natural tilt occurring between the foot plate and vertical support of a typical AFO could aid the affected foot in supination and pronation.
For example, when the AFO connection between the foot plate and vertical support is rigid and unyielding, supination and pronation forces may be transferred to the foot rather than the ankle and/or mid tarsal joints that provide some of the movement required in pronation and supination.
With the movement transferred to the foot, rather than the above-noted joints, the foot, and particularly the heel, may swing in the support plate and tend to become chaffed and sore.
Such limitation of motion may reduce the ability of the foot to act as a shock absorber during heel-strike through foot flat portions of the gait cycle. With the decrease in foot shock absorption, the shock forces of heel strike are translated up the leg to the knee and hip joints, leading to osteoarthritis, pain, and possible limitation of range of motion in the knee and hip.
Additionally, the shock forces absorbed may be translated to the lower back, resulting in lower back pain and possibly disc herniation, particularly in the lumbar spinal area.
Further, during the swing phase of the above-noted left foot, the circumduction of the pelvis translates into rotatory forces on the right foot that is planted on the ground, thereby creating the above-noted supination, that should translate into a torque of the ankle joint and/or mid tarsal joint wherein the right foot tibia circumducts away from the sagittal body plane.
If the foot plate maintains an intrinsic rigidity during gait, the midtarsal area of the foot may be forced to passively supinate against the rigid plate and/or rearfoot, creating undue stress on the midtarsal joint which can result in pain, arthritis and limitation of motion in the midtarsal joint.
Background art, incorporated herein in their entirety by reference, include the following U.S. Pat. Nos.:    1. U.S. Pat. No. 3,916,886, which teaches a preformed drop foot brace;    2. U.S. Pat. No. 4,672,955, which teaches bands formed of curable composite material;    3. U.S. Pat. No. 5,897,515, which teaches an ankle-foot orthosis made of a carbon fiber reinforced material;    4. U.S. Pat. No. 6,102,881, which teaches an upper support bearing against the rear lower leg and a lower support bearing against the rear heel;    5. U.S. Pat. No. 6,361,517, which teaches a foot lift assist comprising an elastic cord anchored at a person's hip by a belt;    6. U.S. Pat. No. 6,790,193, which teaches a dorsal leg shell affixed to a user calf;    7. U.S. Pat. No. 3,680,549 (Lehnels et al);    8. U.S. Pat. No. 2,949,111 (Veikko Samuli Ruotoistenmaki, Vaasankatu);    9. U.S. Pat. No. 6,945,947 B2 (Ingimundarson et al);
Additional background art, incorporated herein in their entirety by reference, include the following U.S. patent applications:    1. Patent Publication No. WO/0135876, teaches a spring attached to the front side of a wearer's leg in a manner that allows sliding of the spring longitudinally; and    2. U.S. Patent Application Publication No. 2007/0197948 A1.